serpin family F member 2, alpha2-antiplasmin inhibitor
Alpha2-antiplasmin inhibitor (A2AP/API, also called plasmin inhibitor/PLI or alpha-2-antiplasmin) is the primary inhibitor of plasmin, a proteinase that digests fibrin, the main component of blood clots. Alpha2AP forms an inactive 1:1 stoichiometric complex with plasmin. It also rapidly crosslinks to fibrin during blood clotting by activated coagulation factor XIII, and as a consequence fibrin becomes more resistant to fibrinolysis. Therefore alpha2AP is important in modulating the effectiveness and persistence of fibrin with respect to its susceptibility to digestion and removal by plasmin. This subgroup corresponds to clade F2 of the serpin superfamily. In general, SERine Proteinase INhibitors (serpins) exhibit conformational polymorphism shifting from native to cleaved, latent, delta, or polymorphic forms. Many serpins, such as antitrypsin and antichymotrypsin, function as serine protease inhibitors which regulate blood coagulation cascades. Non-inhibitory serpins perform many diverse functions such as chaperoning proteins or transporting hormones. Serpins are of medical interest because mutants have been associated with blood clotting disorders, emphysema, cirrhosis, and dementia. A classification based on evolutionary relatedness has resulted in the assignment of serpins to 16 clades designated A-P along with some orphans.
Comment:depending on the conformational state, the RC loop is surface accessible in the active form or buried and inserted as the central beta strand in the inactive form.
Jiyao W et al.(2023). "The conserved domain database in 2023.",